1 files changed, 69 insertions, 0 deletions
diff --git a/test/ruby/test_arity.rb b/test/ruby/test_arity.rb
new file mode 100644
index 0000000000..bd26d5f0f5
--- /dev/null
+++ b/test/ruby/test_arity.rb
@@ -0,0 +1,69 @@
+# frozen_string_literal: false
+require 'test/unit'
+
+class TestArity < Test::Unit::TestCase
+  def assert_arity(expected, method_proc = nil, argc = 0)
+    args = (1..argc).to_a
+    assert_raise_with_message(ArgumentError, /wrong number of arguments \(.*\b(\d+)\b.* (\d\S*?)\)/) do
+      case method_proc
+      when nil
+        yield
+      when Symbol
+        method(method_proc).call(*args)
+      else
+        method_proc.call(*args)
+      end
+    end
+    assert_equal expected, [$1, $2]
+  end
+
+  def a
+  end
+
+  def b(a, b, c, d=1, e=2, f, g, h, i, &block)
+  end
+
+  def c(a, b, c, d=1, e=2, *rest)
+  end
+
+  def d(a, b: 42)
+  end
+
+  def e(a, b:42, **c)
+  end
+
+  def f(a, b, c=1, *rest, d: 3)
+  end
+
+  def test_method_err_mess
+    assert_arity(%w[1 0],     :a, 1)
+    assert_arity(%w[10 7..9], :b, 10)
+    assert_arity(%w[2 3+],    :c, 2)
+    assert_arity(%w[2 1],     :d, 2)
+    assert_arity(%w[0 1],     :d, 0)
+    assert_arity(%w[2 1],     :e, 2)
+    assert_arity(%w[0 1],     :e, 0)
+    assert_arity(%w[1 2+],    :f, 1)
+  end
+
+  def test_proc_err_mess
+    assert_arity(%w[0 1..2],  ->(b, c=42){}, 0)
+    assert_arity(%w[1 2+],    ->(a, b, c=42, *d){}, 1)
+    assert_arity(%w[3 4+],    ->(a, b, *c, d, e){}, 3)
+    assert_arity(%w[3 1..2],  ->(b, c=42){}, 3)
+    assert_arity(%w[1 0],     ->(&block){}, 1)
+    # Double checking:
+    p = Proc.new{|b, c=42| :ok}
+    assert_equal :ok,  p.call(1, 2, 3)
+    assert_equal :ok,  p.call
+  end
+
+  def test_message_change_issue_6085
+    assert_arity(%w[3 1..2])  { SignalException.new(1, "", nil) }
+    assert_arity(%w[1 0])     { Hash.new(1){} }
+    assert_arity(%w[3 1..2])  { Module.send :define_method, 1, 2, 3 }
+    assert_arity(%w[1 2])     { "".sub!(//) }
+    assert_arity(%w[0 1..2])  { "".sub!{} }
+    assert_arity(%w[0 1+])    { exec }
+  end
+end